This invention relates to a combustor for a gas- or liquid-fueled turbine.
A turbine engine typically includes an air compressor, at least one combustor and a turbine. The compressor supplies air under pressure to the combustor(s)--a proportion of the air is mixed with the fuel, while the remaining air supplied by the compressor is utilized to cool the hot surfaces of the combustor and/or the combustion gases, (i.e., the gases produced by the combustion process, and/or other components of the turbine plant).
With the aim of reducing the amount of pollutants produced by the combustion process (particularly No.sub.x), lean burn combustors have been proposed. Such combustors involve the premixing of air and fuel, with a relatively low proportion of fuel being utilized. Combustion then occurs at relatively low temperatures, which reduces the amount of pollutants produced. However, in their basic form such lean burn combustors have a narrow operating range, i.e. they cannot work satisfactorily with large variations in the quantity of fuel being supplied, and are susceptible to flame blow-out or flash-back.
One known solution aimed to overcome difficulties inherent in this type of combustor is to stage the air and/or fuel supply relative to engine load, for example, so that optimum flow and mixture rates are achieved over the whole operating range. Stage combustors have, in the past, taken various designs, from those of fixed geometry which may have a number of burners and to which fuel is selectively directed depending on engine requirements, to those of a more complicated nature which may have movable parts to control the flow of combustion air.
The present invention seeks to provide a three stage combustor of relatively simple construction but which is nonetheless effective in minimizing the production of pollutants resulting from the combustion process and, in addition, operates with good combustion stability and an excellent turndown ratio whilst at the same time giving flashback-free combustion.